A problem of a closed insulating device such as a gas-sealed switchgear in which a high-voltage conductor supported by an insulator is provided in a container in which an insulating gas is sealed therein, is miniaturization by rationalization of insulation design or three-phase integration for cost reduction and environmental load reduction.
The size of the metal container of the closed insulating device is decided by insulation design, thermal design or the like. One of points of the insulation design is to discuss the influence on the insulation performance in the case where a foreign substance exists (adheres) on the inner surface of the metal container.
When a foreign substance exists in the metal container in which the high-voltage conductor supported by the insulator is housed and the insulating gas is sealed, force is generated to the foreign substance due to interaction between charges supplied from the metal container or the like and an operation voltage. Therefore, the foreign substance sometimes moves around in the metal container.
When the closed insulating device is miniaturized, the electric field on the inner surface of the metal container increases and the movement of the foreign substance existing in the metal container is thus likely to become active. The foreign substance, if excessively moving in the metal container, sometimes affects the insulation performance. Further, with a longer shape of the foreign substance, the foreign substance more greatly moves and thus more greatly affects the insulation performance.
For this reason, to prevent the long foreign substance from entering the inside of the metal container, for example, a foreign substance management process is provided to remove the foreign substance in a manufacturing process to thereby enhance the management of the foreign substance. Further, it is necessary to design the electric field intensity on the inner surface of the metal container at the application of the operation voltage to prevent a small foreign substance that is difficult to manage from floating to a height taken into consideration in design or higher and moving around. Here, the height means the distance between the inner surface of the metal container and the foreign substance.
The electric field intensity on the inner surface of the metal container depends on the distance between the high-voltage conductor and the inner surface of the metal container. Therefore, to suppress the floating height of the foreign substance, it is necessary to increase the size of the metal container. This becomes a factor in hindering the miniaturization of the closed insulating device.
There is, as a method of mitigating the influence by the foreign substance, a method of suppressing the movement of the foreign substance. As this method, a method of coating the inner surface of the metal container of the closed insulating device with a highly insulative resin can be exemplified. Coating of the inner surface of the metal container with the resin suppresses the supply of charges from the inner surface of the metal container to the foreign substance to make the foreign substance difficult to move. Further, as the material subjected to the coating of the inner surface of the metal container, an insulating coating material in which particles of a nonlinear resistive material are dispersed in a resin is also under discussion.
The insulating coating material is used not only for the above-described closed insulating device but also for a power generator. A coil conductor of the power generator is at a high voltage, and an iron core of the power generator is at an earth potential. At an iron core outlet of the coil conductor, the potential on the surface of the coil conductor rapidly increases from the earth potential to the high voltage. Therefore, discharge is caused in an edgewise direction of the coil conductor at the iron core outlet. To suppress the discharge, an insulating coating material is used.
In the conventional insulating coating material used for the above-described closed insulating device and power generator, in the case of dispersing the particles of the nonlinear resistive material in the resin, for example, addition of whiskers each having a tetrapod shape is under discussion to ensure a conductive path. Further, the whiskers have been subjected to silane-coupling treatment in order to enhance the wettability with the epoxy resin.
However, in the case of using the conventional insulating coating material as a coating material, the whiskers being an additive and subjected to silane-coupling treatment sometimes aggregate due to addition of a diluting solvent. Therefore, the whiskers exist aggregating on the coating film surface or in the coating film to cause irregularities on the coating film surface. Thus, the insulating coating material cannot sometimes exhibit the nonlinear resistance characteristic which should originally be exhibited.